Given the industrial utility of alkanesulphonyl chlorides, in particular methane sulphonyl chloride, the manufacture of these compounds has formed the subject of several processes, consisting in particular in the photochemical sulphochlorination of alkanes with chlorine and sulphur dioxide. Among these known processes, one particularly effective process for the photochemical sulphochlorination of gaseous alkanes at ambient temperature, for example methane, is the one described in Patents FR 2 578 841 and FR 2 595 095.
This process, which essentially consists in reacting an alkane, sulphur dioxide and chlorine gas mixture in the presence of ultra-violet light delivered by a mercury lamp, is characterized in that the mixture contains a strong excess of sulphur dioxide relative to the alkane, and in that liquid sulphur dioxide is injected into the reaction zone in order to keep the temperature of the latter constant. A plant for implementing this process is also described in the aforementioned patents, the content of which is incorporated here by reference.
In comparison with the photochemical processes of the prior art, which are described in the work by F. ASINGER "Paraffins, Chemistry and Technology", Pergamon Press 1968, p. 520 et seq. and in Patent FR 2 246 520, the process in Patents FR 2 578 841 and FR 2 595 095 has the advantage of not requiring the introduction of any foreign product into the reaction medium, and of forming the latter only with its requisite constituents, namely the alkane, sulphur dioxide and chlorine. Furthermore, this process makes it possible to obtain good conversions and satisfactory yields both with respect to the alkane and with respect to chlorine. Moreover, contributing to better absorption of photons by chlorine and the great ease with which the heat of reaction is dissipated, this process leads to excellent quantum efficiencies and avoids any overheating of the reaction medium.